1. Field of the Invention
The invention relates to a vehicle driving apparatus and a control method of a vehicle driving apparatus. In particular, the invention relates to a vehicle driving apparatus and a control method of a vehicle driving apparatus including an internal combustion engine.
2. Description of the Related Art
Cranking control is executed in which the crankshaft of the internal combustion engine is cranked using an electric motor, when an internal combustion engine is started. Upon such a cranking control, as described in Japanese Patent Application Publication No. 2002-307982 (JP-A-2002-307982), if the temperature is low and thus the viscosity of lubricant is high, the load on the electric motor increases, and thus making it difficult to start the internal combustion engine. Further, low temperature causes a decrease in a voltage of a battery that powers the electric motor, and this further reduces the startability of the internal combustion engine.
A hybrid vehicle, which runs using both an engine and an electric motor(s), accomplishes a high fuel economy, by using the electric motor in an operation region where the fuel economy tends to be low. Therefore, the engine is often not started immediately after start-up of the hybrid vehicle.
However, when the atmospheric temperature is low, the engine is cranked by the electric motor at the same time as the start-up of the hybrid vehicle for heating of the vehicle compartment, system warming-up, and so on. However, because the voltage of the battery decreases at a low temperature, it takes longer to start the engine using the electric motor. Therefore, during the unstable state that is before the engine starts self-driving, a state where the engine is driven by the torque of the electric motor and a state where the engine drives the electric motor alternately occur. That is, the direction of the torque of the electric motor is repeatedly reverses, thereby causing vibrations at the parking lock gear, resulting in producing gear-contact noise between the parking lock gear and the parking lock pawl.